Background: The diagnostic performances of ultrasound (US) examination and US-guided fine needle aspiration (US-FNA) were investigated in thyroid nodules ≤10 mm in size. Methods: From April 2006 to December 2006, 1440 nodules ≤10 mm in size in 1403 patients (mean age, 49.3 years; range, 10-84 years) underwent US and US-FNA. The association between nodule size and inadequate specimen was investigated using the Cochran-Armitage trend test and multivariate logistic regression analysis. To evaluate the diagnostic performances of US and US-FNA, we selected 852 nodules that had undergone surgery, follow-up US-FNA, or follow-up US. A receiver operating characteristic (ROC) curve analysis was used to determine the accuracies of US and US-FNA. Results: Of 1440 nodules, 256 (17.8%) yielded inadequate specimens. As the nodule size increased, the rate of inadequate specimens decreased (P < 0.001). A size of 6 mm demonstrated statistical significance between inadequate and adequate specimens (P < 0.001). The diagnostic accuracy of US was slightly improved as nodule size increased. The false positive rate of US examination was higher in nodules ≤6 mm compared with that of nodules >6 mm in size (P = 0.049). However, US-FNA demonstrated high diagnostic performance in all nodules with adequate specimen. Conclusions: The inadequate specimens of US-FNA and false positives for US examinations increased as nodule size decreased. However, US-FNA demonstrated good diagnostic accuracy, assuming the specimen was adequate.
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